Chemical Solutions (aqueous = water is the solvent)

1. Chemical Solutions (aqueous = water is the solvent) Types of vessels (least to most precise): Beaker Erlennmeyer flask Graduated cylinder Volumetric flask

2. Goals • Make solutions • Dilute solutions • Convert between different concentrations of solutions

3. Facts of Life • Mass is measured in Grams, mg, μg 1g = 1000mg = 1000000µg • Volume is measured in liters, mL, μL 1L = 1000mL = 1000000 μL • Density of water is 1 g / mL

4. Facts of life (cont’d) • Concentration means: amount of solute in a volume of solution • Expressed 3 ways: • 1. percent • 2. mg/ mL • 3. molar

5. Percent Solutions • Per means “for every one” • Cent means 100 • Example: a 5% sugar solution has 5 grams of sugar for 100g of solution

6. Make 250 mL of a 3% starch solution 3 g / 100 g = 3 g / 100 mL because density of water is 1 g / mL Set up a ratio: 3 g / 100 mL = ?g / 250 mL Use 7.5 g of starch and bring to a volume of (BTV) 250 mL with water

7. mg / mL Solutions • 5 mg/mL has 5 milligrams of solute in 1 milliliter of solution

8. Make a 250 mL of a 3 mg /mL starch solution Set up a ratio: 3 mg / 1 mL = ?mg / 250 mL Use 750 mg of starch and bring to a volume of (BTV) 250 mL with water

9. Molar Solutions • 1 mole is 6.02 x 1023 items • Molecular weight or Formula weight is really the mass of 1 mole of molecules (see periodic table) Example: 1 mol of sodium chloride (NaCl) has a mass of 58.44 g.

10. A 1 Molar solution is 1 mol of solute /Liter of solution • Make 250 mL of a 3 molar NaCl solution Set up a ratio: 58.44 g /1 mol = ? g / 3 mol 3 moles has a mass of 175.3 g 3M = 3mol/L = 175.3g/1000mL = ? g/250mL ? = 43.8g BTV of 250 mL

11. Diluting Solutions • Conc A x Vol. A = Conc B x Vol B • Usually want 1 X solutions

12. Solution A is the frozen concentrate Solution B is the 1X juice you drink How concentrated is it? CA VA = CB VB (250mL)(?X) = (1000 mL)(1X) Example: Frozen Orange Juice

13. Answer: Frozen OJ is 4X because ¼ of the final volume is the concentrated oj